1. Field of the Invention
This invention generally relates to laminated fabrics, and more particularly concerns laminated fabrics (laminates) for use in the manufacture of air bags for automobile restraint systems.
2. Description of the Related Art
Polyester and polyamide fabrics having various coatings to reduce permeability are known. U.S. Pat. No. 5,897,929 describes a polyester or polyamide fabric coated with a porosity blocking layer of polyamide material. U.S. Pat. No. 5,110,666 describes a fabric substrate which is coated with a polycarbonate-polyether polyurethane which provides certain permeability, flexibility, toughness and other properties. U.S. Pat. No. 5,076,975 describes a molding operation for forming an elastomer-coated fabric having a defined shape. U.S. Pat. No. 5,763,330 describes a method for extrusion coating a polyethylene resin onto a nylon fabric.
As used herein,“air bag” means inflatable passive safety restraints for automobiles and many other forms of transportation, including military and aviation applications. Air bags are one form of inflatable passive safety restraint device which are now standard in automotive use. Air bags in automobiles must satisfy demanding requirements. Specifically, these requirements include the ability to inflate fully and deflate in milliseconds, or remain partially inflated for several seconds, while fully absorbing passenger impact and providing subsequent pneumatic dampening after impact. The strong and lightweight fabrics used in air bag construction must be relatively airtight, foldable into compact configurations and be resistant to abrasion. Multiple air bag configurations in use include air bags for the front seating area, for side impact protection, for rear seat use, for use in headliner area inflatable curtains, and for use in inflatable seat belts.
The woven fabrics from which air bags are traditionally manufactured may be coated with elastic materials (notably silicone rubber) to manage the air permeability of the fabric. Sticking or blocking of rubber coated fabrics after long term storage in a folded configuration is one of the well known deficiencies of such coated fabrics. Where silicone is applied to the air bag fabric, the application rate of the silicone tends to be quite high, leading to a very flat surface with high friction characteristics which may injure vehicle occupants. As a consequence, such air bag fabric may need to be covered with a non-woven. Alternatives to coatings have been sought over the past few years. Heat shrinking fabrics are one alternative. Calendering the fabric is another alternative. However, these alternatives involve further process steps and more complexity.
EP 1 044 803 A2 discloses a fabric/film laminate for use in air bags. The disclosed laminate films include a polyether block amide, polyurethanes and modified polyolefins. Laminates made with films of polyether block amide are said to be superior to silicone coated fabrics for use in air bag applications in terms of reduced pack volume, reduced wall stiffness and reduced frictional susceptibility. However, there is still a need for fabric/film laminates for use in air bags that provide even lower stiffness so as to be more foldable without at the same time increasing the stickiness of the laminate, which would result in greater undesirable blocking when used in an air bag. There is a further need for fabric/film laminates for use in air bags, which laminates have desirable air permeability characteristics and have a low tendancy to wrinkle.